1. Field of the Invention
The present invention relates to a stepping motor having a molded housing of a synthetic resin which covers an outer peripheral portion of a stator and in which connections of coils wound round bobbins and connector plates are embedded.
2. Description of the Prior Art
Stepping motors are used in various fields, for example as servo motors in flow control valves for the intake of auxiliary air in automobile engines. Particularly, in stepping motors used in places where external vibrations are transmitted to the motors, or in stepping motors used in a highly humid outside air, it is desired that their housings which cover the outer peripheries of their stators be formed by molding using a synthetic resin and that the connections between coils wound round the stator core and terminal plates for connection with an external controller be embedded in a synthetic resin.
As shown in FIG. 1, a stator 102 of a conventional stepping motor 101 is provided with an annular stator core 106, in which silicon steel plates formed by blanking are laminated and fixed. The stator core 106 has on an inner peripheral surface thereof a plurality of axially extending grooves and ridges alternately in the circumferential direction; bobbins 104 formed of an insulating material, which cover both axial ends of the stator core 106 and the surfaces of the grooves; and stator coils 105 wound round the ridges from above the bobbins 104. Both ends of electric wires which constitute each stator coil 105 of the stator 102 are drawn out and connected to plural terminal plates 103. The terminal plates 103 are arranged in two rows to form a male connector 111 and are supported beforehand by a support member 108 formed of a synthetic resin.
The stator 102 and the terminal plates 103 are fixed to a mold (not shown) by which a housing 109 shown in FIG. 1 is formed by injection molding of a synthetic resin. The housing 109 is fixed to a cylindrical outer peripheral surface of the stator core 106. The bobbins 104 at both axial end faces of the stator core 106, exposed portions of the stator coils 105, electric wires drawn out from both ends of each stator coils 105 and connected to the terminal plates 103, and the support member 108, are embedded in the housing 109. Free end portions of the terminal plates 103 are fixed to the housing 109 so as to project to the exterior of the housing, and form a male connector 111 together with a socket wall 110 formed integrally with the housing 109. The numeral 107 in the drawings denotes a metal cover.
In molding the housing 109, in order to place the terminal plates 103 in predetermined positions inside the socket wall 110 to be formed, it is necessary that, with one axial end face (suface M in FIG. 1) of the stator core 106 as a fiducial plane, the support member 108 is to be fixed to the stator core 106 to place one row of the terminal plates 103 at a position where the distance between the row of the terminal plates 103 and the fiducial plane M is set at a predetermined standard distance Ho.
However, since the stator core 106 is a laminate of thin plates formed by blanking and there are variations in the thickness of the plates, an axial distance between the other axial end face P of the stator core 106 and the fiducial plane M is not always the same in all of products. Therefore, when the support member 108 is fixed to the end face P, there is formed a housing 109 wherein the distance from the fiducial plane M to one row of terminal plates 103 is different from a predetermined standard distance Ho, resulting in that a female connector cannot be smoothly engaged with the male connector 111.
Further, when the stator 102 is fixed into a mold for molding, since the electric wires drawn out from the stator coils 105 of the stator 102 to the terminal plates 103 are not fixed, the electric wire may be cut by the flow of resin injected into the mold, or the soldered connection of the electric wires and the terminal plates 103 may be broken.